Android : RxAndroid doesn`t subscribe on new thread

I have task like this:

Observable.just(getMessagesFromDb()).
    subscribeOn(Schedulers.newThread()).
    observeOn(AndroidSchedulers.mainThread()).
    subscribe(incomingMessages -> {
    //do something
    });

where getMessagesFromDb is method synchronously getting messages, without multithreading inside. According to the RxAndroid documentation for subscribeOn method:

Asynchronously subscribes Observers to this Observable on the specified Scheduler

And there is my question - why is the database request executed on main thread? How to do it asynchronously?